Climate change

Climate change is a long-term shift in the average weather patterns that define Earth’s climates, including temperature, precipitation, and wind patterns, measured over decades rather than days or years. Since the mid-20th century, human activity, chiefly the burning of fossil fuels, has been the main driver of the changes scientists have observed, though natural factors such as volcanic activity, ocean cycles, and variations in the Sun’s output also influence climate over time.

History of climate change science and policy

Scientific concern moved from individual researchers to formal international coordination in 1988, when the United Nations Environment Programme and the World Meteorological Organization jointly established the Intergovernmental Panel on Climate Change, later endorsed by the UN General Assembly. The IPCC’s First Assessment Report in 1990 helped lead to the 1992 UN Framework Convention on Climate Change, and its Second Assessment Report informed the 1997 Kyoto Protocol, the first treaty to set binding emissions targets for developed countries. The IPCC’s Fourth Assessment Report in 2007 focused attention on limiting warming to 2 degrees Celsius above pre-industrial levels and led to the panel sharing that year’s Nobel Peace Prize with former US Vice President Al Gore. Its Fifth Assessment Report, published in 2013 and 2014, supplied the scientific basis for the 2015 Paris Agreement, under which nearly every country committed to limiting warming well below 2 degrees Celsius and pursuing efforts to limit it to 1.5 degrees.

Climate change versus weather

Weather describes atmospheric conditions over short periods, from minutes to days, in a specific place. Climate describes long-term averages of temperature, humidity, and rainfall, typically measured over at least 30 years across a region or the whole planet. A single unusually cold winter says little about climate change in either direction, because climate change is defined by sustained shifts in long-term averages and extremes, not by any one weather event.

How climate change happens

Burning fossil fuels raises the concentration of heat-trapping gases in the atmosphere, strengthening the greenhouse effect beyond its natural baseline and raising Earth’s average surface temperature. The Intergovernmental Panel on Climate Change estimates that human emissions have already warmed the climate by nearly 1.1 degrees Celsius since the 1850 to 1900 period, and global average temperatures are projected to reach or exceed 1.5 degrees Celsius of warming within the next few decades on current trends. Burning fossil fuels for energy and transportation is also a major source of conventional air pollution, so the two problems share many of the same root causes and, often, the same solutions.

Effects of climate change

Global sea level has risen about 8 inches since 1880, driven by melting land ice and the expansion of seawater as it warms, with at least another foot of rise projected by 2100 and significantly more under high-emissions scenarios. Glaciers, ice sheets, and Arctic sea ice are all shrinking, and current projections suggest the Arctic Ocean could become largely ice-free in late summer before mid-century. Climate change has roughly doubled the area burned by wildfires in parts of the western United States in recent decades and is projected to intensify hurricane rainfall and strength, while shifting precipitation patterns unevenly, bringing more rain to some regions and worsening drought in others. Plant and animal ranges are shifting toward higher latitudes and elevations, growing seasons are lengthening in ways that affect both ecosystems and agriculture, and some changes, especially to ice sheets and sea level, are expected to continue for centuries even if emissions stopped today.

Fisheries, freshwater ecosystems such as the Great Lakes, and forests already weakened by drought, wildfire, and insect outbreaks face growing compounded risks as these individual pressures increasingly overlap in the same places at the same time, rather than arriving one at a time as separate, more manageable events.

Why climate change matters, and the policy response

Because future severity depends heavily on how much more carbon dioxide humanity emits, every ton of reduced emissions genuinely narrows the range of worse outcomes, which is the scientific logic behind tracking individual and organizational carbon footprints alongside national policy targets. The distinction between “climate change” and “global warming” matters for precision: global warming refers specifically to the long-term rise in average surface temperature, while climate change captures the broader set of related shifts, in precipitation, storms, and ecosystems, that this warming sets in motion.

Responses to climate change generally fall into two complementary categories. Mitigation means reducing or preventing greenhouse gas emissions in the first place, through steps such as shifting to renewable energy, improving energy efficiency, and protecting forests and other natural carbon sinks. Adaptation means adjusting to changes that are already happening or are now considered unavoidable, such as building sea walls, developing drought-resistant crops, or redesigning infrastructure to handle more intense storms. Most national and international climate strategies, including the Paris Agreement, pursue both tracks at once, since even an ambitious reduction in emissions would still leave a certain amount of further warming already locked in by gases already in the atmosphere.

FAQs

Is climate change the same everywhere on Earth? No. Average global temperature rise masks significant regional variation; the Arctic, for example, is warming several times faster than the global average, while some ocean regions have warmed more slowly, which is why climate scientists study regional projections separately from the single global average figure.

Can climate change be reversed? Not quickly. Carbon dioxide can remain in the atmosphere for centuries, so even a complete stop to emissions today would not immediately reverse warming already underway; most of the changes already set in motion, particularly to sea level and polar ice, are expected to continue for centuries regardless of future emissions choices.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 1, 2026Researched and drafted with AI assistanceReport an issue